During Main Mission 08, you will find some “elevators,” which are really just rocks that move upward through some blood. When you get to the second elevator, ride it up about halfway and you might notice a ledge off to the right side. Double jump and use Gerbera’s dodge to boost yourself to this ledge. From here, turn the camera so you will see a Grim Grip point moving up and down. Shoot it to lock the thing in place, preferably at the top of its range, then do the same with the second while you’re in mid-air. This should hopefully bring you to a ledge at the very top of the room, where you can drop down into a large room with nothing really in it. Look for the familiar glowing red spot, stand on it, and look back where you dropped in to find the markings for the Secret Mission.
For this Secret Mission, you have to get to the goal (the Blue Orb Fragment) without touching the ground. Once you’re in the air, touching the ground will result in failure, so you’ll have to start from the beginning. You will be using Grim Grip points to do this and they can be finnicky at times, especially since you have to shoot each one to open them after the first. Although it might not make a difference, holding forward on the left analog stick could push you forward after launching from a Grip point. It will take a bit of time to get the timing down on each grapple point. Note that you only have a single double jump throughout the entire thing, should you have purchased Air Hike, so you can’t simply use it throughout the entire Secret Mission.
Also, don’t be alarmed when you get to the open area, as the one Grip point will launch you high into the air. It’s best to save the double jump for when you really need it and not use it right off the bat. Lastly, you shouldn’t need to adjust anything at the end, as you will land right on the Blue Orb Platform.